Why is the center of gravity of an aircraft with longitudinal stability located in front of the center of pressure?

The design with the aircraft center of gravity in front of the aerodynamic center is called static stability design.

Static stability design is a traditional aircraft design mode. When the center of gravity of the aircraft is in front of the aerodynamic center, it needs to rely on the horizontal tail to generate downward negative lift for trimming, so that the aircraft can maintain a level flight state.

If the horizontal tail continues to add negative lift, the aircraft will be in a nose-up state.

If the horizontal tail removes negative lift, the aircraft will nose down.

Conventional static stability design enables the aircraft to have the ability to self-correct. The technical difficulty and design difficulty are relatively low. The control system is relatively simple. It does not require a too complex computer-aided system. The cost is relatively low and it is easy to realize manual control.

However, the static stability design has a large lift loss, the overall lift efficiency is not high, the sensitivity is poor, and the maneuverability is usually not ideal.

This is especially a fatal flaw for fighters with high mobility requirements.

Therefore, modern fighters have all adopted the design idea of ??moving the center of gravity to a certain position behind the aerodynamic center. This design is called relaxed static stability design.

The relaxed static stability design greatly improves the aircraft's aerodynamic efficiency and sensitivity.

However, the design is difficult and maneuverability must be achieved through a computer-aided stabilization system.

Currently popular internationally is the highly mature three-axis four-redundancy flight control system.